This invention relates to a tire and wheel rim assembly and in particular to tubeless pneumatic tire and wheel rim assemblies.
In conventional pneumatic tire and wheel rim assemblies the tire beads are retained on their respective bead seats by means of the internal air pressure and commonly by the bead seats being tapered and/or the use of a safety hump.
Deflation of the tire, however, or operation in a partially deflated state leaves the assembly in a relatively unsafe condition in which the tire beads may be moved from their respective bead seats by sideways force. Such a condition may affect the control and safety of the vehicle and in the case of the commonest types of wheel rim having a well to allow the tire fitting, there is a grave danger of complete separation of the tire from its wheel rim and/or contact of the wheel rim flange with the road surface. Both these conditions are dangerous.
Many suggestions have been made to deal with this problem including bead spacer rings and the tire and wheel rim assembly known as the TD tire which is disclosed in U K Patent Specification No. 1584553.
The latter TD type of construction uses a circumferentially extending groove in the wheel rim adjacent to the bead seat and a radially and axially projecting toe on the tire engaging in the groove. This construction, however, requires a larger well in the wheel rim than in a conventional assembly which reduces the usable volume within the wheel for brake space and also has a severe problem in compatibility in that the fitting of a tire without the necessary projecting toe to the TD type of wheel rim gives an assembly which has a reduced bead retention property to a standard tire on a standard wheel rim. This reduction in bead retention properties of a standard tire on the wheel rim so far has made it essential for the diameter of the TD type of tire and wheel rim to be made different from the normally accepted inch diameter tire and wheels to ensure this mis-match cannot occur in practice. This has limited the adoption of the TD bead retention system.
Another prior art approach to the problem is disclosed in U K Patent Specification 2026957 which uses a tire bead having a sector of the main bead region, which is the axially and radially inner portion of an otherwise normal bead, constructed so that progressive rotation of the bead generates a substantially increasing compression in the bead and thus a continually increasing tension in the bead hoop. This can be done either by an increase in hardness around the sector or a progressive increase in dimension. The specification requires an additional friction increasing means between the tire contacting portion of the bead seat and the region of the bead seat which contacts the wheel rim in the normally seated condition to ensure the necessary rotation without relative slippage. Friction increasing means disclosed include knurling or other mechanically formed grooving or teeth on the bead seat of the wheel rim and thus the disclosure teaches an assembly having a bead seat on the rim which is not suitable for a standard tire bead because of the specially machined bead seat. The tire bead shape is not conducive to correct and secure seating or sealing of the assembly. Also reliance is made on frictional grip once the bead has rotated beyond its initial rest position and the wheel rim cannot be used for a normal tire.
In each case of the prior art, whilst some retention may be provided, true compatibility with tires not of the required construction has not so far been achieved and in each case either the special tire cannot be used on a standard type rim, a standard tire cannot be used on the special rim or both.